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For applications that require data compression, the functions in this module
allow compression and decompression, using the zlib library. The zlib library
has its own home page at http://www.zlib.net. There are known
incompatibilities between the Python module and versions of the zlib library
earlier than 1.1.3; 1.1.3 has a security vulnerability, so we recommend using
1.1.4 or later.

zlib’s functions have many options and often need to be used in a particular
order. This documentation doesn’t attempt to cover all of the permutations;
consult the zlib manual at http://www.zlib.net/manual.html for authoritative
information.

Computes an Adler-32 checksum of data. (An Adler-32 checksum is almost as
reliable as a CRC32 but can be computed much more quickly.) The result
is an unsigned 32-bit integer. If value is present, it is used as
the starting value of the checksum; otherwise, a default value of 1
is used. Passing in value allows computing a running checksum over the
concatenation of several inputs. The algorithm is not cryptographically
strong, and should not be used for authentication or digital signatures. Since
the algorithm is designed for use as a checksum algorithm, it is not suitable
for use as a general hash algorithm.

Changed in version 3.0: Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use adler32(data)&0xffffffff.

Compresses the bytes in data, returning a bytes object containing compressed data.
level is an integer from 0 to 9 or -1 controlling the level of compression;
1 (Z_BEST_SPEED) is fastest and produces the least compression, 9 (Z_BEST_COMPRESSION)
is slowest and produces the most. 0 (Z_NO_COMPRESSION) is no compression.
The default value is -1 (Z_DEFAULT_COMPRESSION). Z_DEFAULT_COMPRESSION represents a default
compromise between speed and compression (currently equivalent to level 6).
Raises the error exception if any error occurs.

Returns a compression object, to be used for compressing data streams that won’t
fit into memory at once.

level is the compression level – an integer from 0 to 9 or -1.
A value of 1 (Z_BEST_SPEED) is fastest and produces the least compression,
while a value of 9 (Z_BEST_COMPRESSION) is slowest and produces the most.
0 (Z_NO_COMPRESSION) is no compression. The default value is -1 (Z_DEFAULT_COMPRESSION).
Z_DEFAULT_COMPRESSION represents a default compromise between speed and compression
(currently equivalent to level 6).

method is the compression algorithm. Currently, the only supported value is
DEFLATED.

The wbits argument controls the size of the history buffer (or the
“window size”) used when compressing data, and whether a header and
trailer is included in the output. It can take several ranges of values,
defaulting to 15 (MAX_WBITS):

+9 to +15: The base-two logarithm of the window size, which
therefore ranges between 512 and 32768. Larger values produce
better compression at the expense of greater memory usage. The
resulting output will include a zlib-specific header and trailer.

−9 to −15: Uses the absolute value of wbits as the
window size logarithm, while producing a raw output stream with no
header or trailing checksum.

+25 to +31 = 16 + (9 to 15): Uses the low 4 bits of the value as the
window size logarithm, while including a basic gzip header
and trailing checksum in the output.

The memLevel argument controls the amount of memory used for the
internal compression state. Valid values range from 1 to 9.
Higher values use more memory, but are faster and produce smaller output.

zdict is a predefined compression dictionary. This is a sequence of bytes
(such as a bytes object) containing subsequences that are expected
to occur frequently in the data that is to be compressed. Those subsequences
that are expected to be most common should come at the end of the dictionary.

Changed in version 3.3: Added the zdict parameter and keyword argument support.

Computes a CRC (Cyclic Redundancy Check) checksum of data. The
result is an unsigned 32-bit integer. If value is present, it is used
as the starting value of the checksum; otherwise, a default value of 0
is used. Passing in value allows computing a running checksum over the
concatenation of several inputs. The algorithm is not cryptographically
strong, and should not be used for authentication or digital signatures. Since
the algorithm is designed for use as a checksum algorithm, it is not suitable
for use as a general hash algorithm.

Changed in version 3.0: Always returns an unsigned value.
To generate the same numeric value across all Python versions and
platforms, use crc32(data)&0xffffffff.

Decompresses the bytes in data, returning a bytes object containing the
uncompressed data. The wbits parameter depends on
the format of data, and is discussed further below.
If bufsize is given, it is used as the initial size of the output
buffer. Raises the error exception if any error occurs.

The wbits parameter controls the size of the history buffer
(or “window size”), and what header and trailer format is expected.
It is similar to the parameter for compressobj(), but accepts
more ranges of values:

+8 to +15: The base-two logarithm of the window size. The input
must include a zlib header and trailer.

0: Automatically determine the window size from the zlib header.
Only supported since zlib 1.2.3.5.

−8 to −15: Uses the absolute value of wbits as the window size
logarithm. The input must be a raw stream with no header or trailer.

+24 to +31 = 16 + (8 to 15): Uses the low 4 bits of the value as
the window size logarithm. The input must include a gzip header and
trailer.

+40 to +47 = 32 + (8 to 15): Uses the low 4 bits of the value as
the window size logarithm, and automatically accepts either
the zlib or gzip format.

When decompressing a stream, the window size must not be smaller
than the size originally used to compress the stream; using a too-small
value may result in an error exception. The default wbits value
corresponds to the largest window size and requires a zlib header and
trailer to be included.

bufsize is the initial size of the buffer used to hold decompressed data. If
more space is required, the buffer size will be increased as needed, so you
don’t have to get this value exactly right; tuning it will only save a few calls
to malloc().

Changed in version 3.6: wbits and bufsize can be used as keyword arguments.

Compress data, returning a bytes object containing compressed data for at least
part of the data in data. This data should be concatenated to the output
produced by any preceding calls to the compress() method. Some input may
be kept in internal buffers for later processing.

All pending input is processed, and a bytes object containing the remaining compressed
output is returned. mode can be selected from the constants
Z_NO_FLUSH, Z_PARTIAL_FLUSH, Z_SYNC_FLUSH,
Z_FULL_FLUSH, Z_BLOCK (zlib 1.2.3.4), or Z_FINISH,
defaulting to Z_FINISH. Except Z_FINISH, all constants
allow compressing further bytestrings of data, while Z_FINISH finishes the
compressed stream and prevents compressing any more data. After calling flush()
with mode set to Z_FINISH, the compress() method cannot be called again;
the only realistic action is to delete the object.

A bytes object which contains any bytes past the end of the compressed data. That is,
this remains b"" until the last byte that contains compression data is
available. If the whole bytestring turned out to contain compressed data, this is
b"", an empty bytes object.

A bytes object that contains any data that was not consumed by the last
decompress() call because it exceeded the limit for the uncompressed data
buffer. This data has not yet been seen by the zlib machinery, so you must feed
it (possibly with further data concatenated to it) back to a subsequent
decompress() method call in order to get correct output.

Decompress data, returning a bytes object containing the uncompressed data
corresponding to at least part of the data in string. This data should be
concatenated to the output produced by any preceding calls to the
decompress() method. Some of the input data may be preserved in internal
buffers for later processing.

If the optional parameter max_length is non-zero then the return value will be
no longer than max_length. This may mean that not all of the compressed input
can be processed; and unconsumed data will be stored in the attribute
unconsumed_tail. This bytestring must be passed to a subsequent call to
decompress() if decompression is to continue. If max_length is zero
then the whole input is decompressed, and unconsumed_tail is empty.

All pending input is processed, and a bytes object containing the remaining
uncompressed output is returned. After calling flush(), the
decompress() method cannot be called again; the only realistic action is
to delete the object.

The optional parameter length sets the initial size of the output buffer.